I don't remember who originally stated it, but there is an old axiom that "There are three stages of Reading: 1. Infantile - to learn about the world, 2. Adolescent - to learn about oneself, and 3. Adult - to read simply for enjoyment".

I think a lot of the current market for (adult) books reflects the second stage. It would be interesting to ask the person(s) sitting next to you on the next plane ride why they are reading, e.g. Malcolm Gladwell vs Dan Brown vs Ian McEwan.